Electrically conducting surface and method for producing same



July l, 1952 R. A'. GAlsER I 2,602,032

ELECTRICALLY coNDucTING SURFACE: Aun METHOD Foa PRonUcIN'G SAME Filed Aug. 19, 1946 TTGIZ Patented July 1, V1952 UNirrao STAT-Es Aoiff-rali:cflsy ELECTRICALLY 'CONDUCTING-S1UREACE AND. o

METHOD FOR' PRODUCIN G .'SAME E Ohio, a-corporatonof Ohio" ApplicationAugustlS, 1946,-Serial No. 691,636

perfectly transparent glass fsheet canV beI madev capable of 'conducting- 'a' substantial current of electrcity'without interfering with its naturall propertiesof light transmission; clarity of vision,A and absence of color. Similarly, Viigured, colored; and otherv glass articles of distinctive appearance may'haveall ror any part of their-surfacestreated, to "render them electrically' conducting; without noticeably altering their.v original appearance:l

' Transparent, colorless, electrically conducting films are disclosed in an application of Gaser etal., Serial No. 513,144, led"De`cemb'er`6,'-1943, and'now abandoned, andintwo Gaiser applications-'Serial Nos. 654,473 and"654',47`4, lbothiiled May 1'4, 1946. In these earlier led'casesthekele tricallyA conducting lm is a transparent coating of tinjoxide, 'applied directly to thesurfacefof -a glass i'loody, byCOating or `iuming4 it with 'a tin4 halide;

Such lms; when appliedto thebody'will ree' duce :the electrical 'resistance'` of the' 'glass' from 1,0ll0,000,000,000 `ohms,1per. squarearea; to -around 50;'000 ohms. Or, differently` expressed, they will increase the electrical. conductivity of 4the-untreated glass some twenty milliontimes; Films of this kind wereproduced on a' commercial basis; forthearmy and =navy during therlate War, and proved extremelyvaluable 'for purposes 'of electro; static dissipation.

The. electrical resistance of these direct contact, transparenttin oxidelmsrcouldlbe 'further reduced, according vto the.disclosureof;the previous applications, Yby subjecting the. Aglass :surfaceto theactionlof the tin halide fora longerperiod of time. YPractically invisible coatingshavinga coefficient of electrical resistance as Ylovv as 30,000 ohms per square area could be produced in this manner; however, increased-exposure to the f-tin halide also,;acted .to;develop`=color-fand to reduce transparency in the resulting lm.

'Nowit is` they aim lof* fthepresenttinventionito provide a new and different method of reducing`fthev electrical resistance in 'a vtransparentelectrically vconducting "lmg-Y and:v one =whichffhaslrlittlef or'noJ effect l on the transparency of the'iillmzt..

Brie'yf stated; thisnovel 1 method fcomprlsessdea positinga transparent basefcoating-derived tromsilica-*on th'eglass lor other-surface tof'beftreatcd; and then applyingS y the-'1 electrically-conducting coating over the1bas`efc'oat'.`

In Y other words, another 'importantfobject .1 of-J theinvention -'is theprovision lo'i amultilayerlm comprising a transparent' sili'caftype ibase-f'coat; and. "a transparent -topf 'coatl ofanfelectlcal cone: ductingfmaterial. Byfthis' imeans; Aresistances:of less-than 1'000 ohms-perL-square'area canibeprof-V duced on Yglass surfaces-Withoutidecreasingfftliei light`ftransmission1to-` anpbjectionable fdegrear.v

' 'Other objects and :advantagesofftliel inventionwill become moref'apparent duringfthe-courseffof the following description,-when-*taken-fin,connec-- Fig; 2 is avertical sectional-.view fthrouglri-a" heating'oven 'with a-glass sheet suspendedftlferein; and

' Figi is a'verticalsectionthrough-faffuniirigly chamber, showing'- a glass`- sheet-being exposedftothe vapors Aof a tin chloride:- V

The novel feature of 'my'linventionfresids-pri-i: marilyV in the fact that'theelectrically' conducting lm employed-is not--applieddrect1yto fthe suraface to be treated.l Instead,- it `is'depositedover athin; :transparentbase coat that Iis'interpose'd between Ythe surfacel and* thefffllm.- :Preferably sheets. ina numbeno'f different ways,. 'Tlermal" vacuum evaporation of fused silica andcry'stalline quartz, hydrolysis of silicon tetrachloride, and hydrolysis of organic silicates such as ethyl silicate were all used as the means of securing a silica lm on a glass surface that would not interfere with the desirable properties of the finished product.

However, the best method that has been found to date involves the use of water solutions of silicates; for example, sodium silicate or potassium silicate.

It is important to note that when silicate solutions are diluted with water a hydrosol is formed, which changes slowly in the laboratory atmosphere to a hydrogel. This change is accompanied by a slow change in the silicate structure and I feel that it has an important bearing on the nal properties of the film.

To illustrate, I prefer for the purpose a solution of one part of potassium silicate and seven parts of water by volume, with the potassium silicate having an alkali-silica ratio of 1:3.9232 Baum.

- Now, if a light of clean glass is dipped into this solution immediately after it is prepared, and then filmed with tin chloride, a lower resistance than would be obtained without the silica treatment is noted. However, if the silicate solution is first allowed to stand for four hours, and the glass then treated in exactly the same manner described above, it will be found that an even greater reduction in electrical resistance is obtained.

The four-hour time interval between mixing the silicate solution and `using it to apply a base coat to the glass has been found to be a very good one. Nevertheless, I do not wish to give the impression that this is necessarily the very best interval that can be used. As a matter of fact, we have noted, in plotting time intervals against increased conductivity factors, that rather symmetrical curves are obtained which show peaks at several time intervals.

Nevertheless, We have standardized on the fourhour aging interval in our production and, for the purposes of illustration, the procedure which I usually follow in practicing the method of the invention is set forth below:

`Clean glass is immersed in an approximately four-hour old silicate solution composed of sodium silicate and/or potassium silicate in a Water medium. Rather wide variation in both the silicate and water content can be made without destruction of the beneficial results of the process. However, I prefer to utilize a room temperature solution of one part of Kasil #2 in seven parts of distilled water by volume.

The dipping procedure is shown diagrammatically in Fig. 1. As indicated there, a glass sheet I0, after cleaning, is suspended from tongs I I and then lowered into the silicate solution I2 contained in a suitable tank I3. The dipped sheet is mechanically withdrawn from the solution, as by the cable I4, at a uniform and rather slow rate, to insure the maximum uniformity of coating. After removal from the bath the sheet, coated with the silicate solution, is dried for a few minutes, whereupon it is ready to receive the electrically conducting coating. l

The invention is not restricted to the use of any specific transparent, electrically conducting film, nor to any specific method of producing such a film. Thus, any of the methods, and their resulting lms, that have been disclosed in the three applications referred to above may be used in completing the multilayer coating. 4

Ordinarily, I prefer the method of application 513,144, wherein a heated surface is exposed to the vapors of stannic tetrachloride, as the means of applying the electrically conducting film. Thus, following this process, the coated and dried sheet Ill' is introduced into an oven I5, as shown in Fig. 2, which is preferably maintained at a temperature around 1200 degrees Fahrenheit.

Within the furnace I5, the sheet I0 should be heated to substantially the point of softening of the glass. Because glass varies and has no precise softening point, it is not practical to give any exact temperature requirements; but, in securing colorless, transparent, electrical conducting surfaces on average coated glass, it has been found that exposure of the glass to temperatures between 550 to 700 degrees centigrade for from two to ten minutes, followed by `nnmediate exposure to the vapors of the tin halide, give very satisfactory results. Perhaps the best general statement that can be given is that the glass should be heated sufciently to be relieved of strains Without change of Vdimensions or contour.

After proper heating, the glass sheet I0 is removed from the furnace I5 and introduced into the fuming chamber I6 of Fig. 3, where it can be exposed to the fumes of stannic tetrachloride. Stannic tetrachloride is an extremely volatile liquid, and, by pouring a sufficient quantity into a container Il in the bottom of the chamber I6, the atmosphere in the chamber will become saturated with the vapors of the compound. The hot glass sheet IB is suspended in this saturated atmosphere and moved gently back andforth, for a period of time varying from four to twelve seconds. The average time is about six seconds. But the important thing is that the coated glass be exposed to the stannic chloride vapors long enough to secure an electrical conducting surface, and be removed before any noticeable fog, cloud or color appears.

After removal from the fuming chamber, the glass may be cooled in the air at normal temperature, it may be slowly annealed, or, it may be suddenly chilled to place its outer surfaces under compression and the interior under tension.

The chemical action which takes place when the hot coated glass is exposed to the vapors of the tin halide is not completely understood, but it is believed that it is the presence of stannic oxide that is responsible for the peculiar proper'- ties of the top film. As to the base lm, this is applied as a silicate, but under the heat necessary to the fuming process it is appreciated that the nal undercoat may be of silica.

At any rate, glass treated in the manner just described will be transparent, colorless, and will possess electrical conductivity superior to glass treated with stannic tetrachloride alone. That this is actually the case has been proven thousands of times in the course of my work by the simple expedient of covering only one-half of a glass sheet with a silica derived coating and then applying the electrically conducting film over the entire sheet. n

When this has been done the electrical resistance of the two adjacent areas, one with the base film and the other Without it, is measured. By dividing the resistance of the area having the electrically conducting nlm over the base coat, a factor is obtained which denotes the number of times greater conductivity the base coated area has.

Factors of the` order of 10 are common and factors as high as 23+ are often noted.

Such increased conductivity is extremely important in transparent, electrically conducting films because it permits higher amperages to be directed through the fil-ms with lower voltages.

It is to be understood that the form of the invention herewith shown and described is to be taken as a preferred embodiment of the same, and that various changes may be resorted to without departing from the spirit of the invention or the scope of the subjoined claims. For example, intermediate coatings might be applied between the top and base coat.

I claim:

1. The method of producing an electrically conducting coating on a surface, which comprises applying a solution of a silicate to said surface, heating said surface to substantially its point of softening, and then applying a tin halide in fluid form.

2. The method of increasing the electrical conductivity of a transparent electrically conducting film on a surface, which comprises forming a transparent coating of silica on said surface before applying the electrically conducting film.

3. The method of increasing the electrical conductivity of a transparent electrically conducting `film on a surface, which comprises first applying a transparent coating of a silicate on said surface and then applying the electrically conducting film.

4. The method of increasing the electrical conductivity of a transparent electrically conducting lm on a surface, which comprises first applying a transparent coating of potassium silicate on said surface and then applying the-electrically conducting film.

5. The method of increasing the electrical conductivity of a transparent electrically conducting film on a surface, which comprises applying a transparent coating of sodium silicate on said surface before applying the electrically conducting film.

6. The method of producing a transparent electrically conducting coating of relatively low electrical resistance on a surface, which comprises forming a transparent coating of silica on said surface, and then applying a transparent film of tin oxide over said coating.

7. The method of producing a transparent electrically conducting coating of relatively low electrical resistance on a surface, which comprises applying a transparent coating of a silicate on said surface, and then forming a transparent electrically conducting lm of tin oxide over said coating.

8. The method of producing a transparent electrically conducting coating of relatively low electrical resistance on a surface, which comprises applying a transparent coating of potassium silicate on said surface, and then forming a transparent electrically conducting film of tin oxide over said coating.

9. The method of producing a transparent electrically conducting coating of relatively low electrical resistance on a surface, which comprises applying a transparent coating of sodium silicate on said surface, and then forming a transparent lm of tin oxide over said coating.

10. The method of producing a transparent electrically conducting coating of a relatively low electrical resistance on a glass surface, which comprises coating said surface with a transparent layer of silica, heating the silica coated surface,

and then exposing the hot coated surface to the filming action of a tin chloride.

11. The method of producing a transparent electrically conducting coating of a relatively low electrical resistance on a glass surface, which comprises coating said surface with atransparent layer of a silicate, and then exposing said surface while at a temperature approximating its point of softening to the action of a tin chloride in fluid form.

12. The method of producing a transparent electrically conducting coating of a relatively low electrical resistance on a glass surface, which comprises coating said surface with a transparent layer of potassium silicate, heating the coated surface to substantially the softening point of the glass, and then exposing the hot coated surface to the vapors of stannic tetrachloride.

13. The method of producing a transparent electrically conducting coating of a relatively low electrical resistance on a glass surface, which comprises coating said surface with sodium silicate, heating the coated surface to substantially the softening point of the glass, and then exposing the hot coated surface to the vapors of stannic tetrachloride.

14. The method of producing a transparent electrically conducting coating of a relatively low electrical resistance on a vitreous surface, which comprises coating said surface with potassium silicate, heating said coated surface to substantially the softening point of the vitreous material, and then exposing the hot coated surface to the action of a tin chloride in iiuid form until said electrically conducting film is formed.

15. The method of producing an electrically conducting coating on a surface of a vitreous body which comprises applying an aged solution of a silicate to said surface, heating the coated surface to a temperature approximating the softening point of the vitreous material of the body, and then applying a tin halide in uid form to said hot surface.

16. An electrically conducting film of tin oxide on a surface, and a layer of silica between said surface and said film.

17. A transparent electrically conducting film on a surface, comprising a base layer of a silicate and a top layer of electrically conducting tin oxide.

18. A multilayer electrically conducting coating on a surface, comprising a base layer of potassium silicate and a top layer of electrically conducting tin oxide.

19. An electrically conducting film of tin oxide on a surface, and a layer of sodium silicate between said surface and said film.

ROMEY A. GAISER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,118,795 Littleton May 24, 1938 2,281,474 Cartwright et al. Apr. 28, 1942 2,290,911 Jones July 28, 1942 2,337,460 French Dec. 21, 1943 2,356,553 Weissenberg Aug. 24, 1944 2,429,420 McMaster Oct. 21, 1947 

1. THE METHOD OF PRODUCING AN ELECTRICALLY CONDUCTING COATING ON A SURFACE, WHICH COMPRISES APPLYING A SOLUTION OF A SILICATE TO SAID SURFACE, HEATING SAID SURFACE TO SUBSTANTIALLY ITS POINT OF SOFTENING, AND THEN APPLYING A TIN HALIDE IN FLUID FORM. 